1. Field of the Invention
The present invention relates to a rotating electric machine including a rotor divided into a plurality of blocks in an axial direction of the rotor, which are arranged to be offset in a circumferential direction of the rotor.
2. Description of the Related Art
In a synchronous motor including an interior permanent magnet rotor having permanent magnets embedded in an outer circumferential region of a rotor core, the distribution of a magnetic field generated between a stator and the rotor is not an ideal sine wave distribution in a gap between the stator and the rotor, and magnetic saturation occurs in the rotor core due to the magnetic field. For those reasons, when the rotor is rotated, the magnetic flux distribution density in the gap between the stator and the rotor does not exhibit a smooth profile, and hence torque pulsation such as cogging torque and torque ripples occurs in the rotor. This torque pulsation may cause vibration and noise at the time of running the synchronous motor, and hence the torque pulsation needs to be minimized.
Hitherto, there has been known a rotating electric machine that is suppressed in torque pulsation (see, for example, Japanese Patent Application Laid-open No. 2004-248422). In this rotating electric machine, the rotor core is divided into a plurality of blocks in the axial direction, and the blocks are arranged to be offset in the circumferential direction so that a multi-step skew is formed in the rotor.
However, the blocks are arranged to be offset in the circumferential direction, and hence a part of the magnetic flux generated in a radially-outer side surface (for example, an N pole) of the permanent magnet of one of the adjacent blocks may flow in the axial direction and pass through a stator core of the other of the adjacent blocks, with the result that the magnetic flux may enter a radially-inner side surface (for example, an S pole) of the permanent magnet of the other of the adjacent blocks. Thus, it becomes difficult to obtain an effect of reducing the torque pulsation at a skew angle to be derived theoretically. Further, the magnetic flux passing through the stator core is reduced, thus leading to a problem in that the torque reduction of the rotating electric machine becomes significant.